quartet, quatuor [F], quartett [G], quartetto [I]—ensemble or work for four players the most important examples being the string quartet and the piano quartet

semplice [I], con semplicità—simple, unaffected

string quartet, Streichquartett [G], quatuor à cordes [F], quartetto d'archi [I], quartetto di cordi [I]—an ensemble as well as music written for that ensemble comprising 2 violins, viola and cello. This is one of the essential genres / forms / ensembles of chamber music and arguably a critical "core" of "classical" music. Explore the string quartet.

tema con variazioni, con variazioni, Tema e variazioni, theme and variations, Thema mit Variationen [G], Thème varié [F]—a common movement form featuring an initial theme followed by a series of variations on that theme, each of which adjusts any number of parameters to achieve variety, e.g. tempo, rhythm, key, instrumentation, etc.A challenge to the composers ingenuity and a delight for the listener

theme, tema [I]—a complete and recognizable musical entity (e.g. melody) used as the basis for elaboration (e.g. variations, sontata, fugue, etc.). Also called a subject. Motif (motive) is generally a smaller fragmentary entity.

variation, variazione, variatio, variato, variata—a modified re-iteration of a previous theme, reprise, couplet, etc. The music is varied, embellished or creatively transformed for variety while maintaining a unity relationship with the original. See "Theme and Variations."